SBB´s network is almost fully electrified. Diesel engines are only used in short distance switching work and at sidetrack connections to industrial railroads. These pictures show mainly rail tractors used for maintenance work and diesel switching engines.

Two SBB Am 841 diesel locomotives and one Re 4/4 II series electric locomotive (in its original dark green livery) at Porrentruy station. The Am 841 is a fairly new locomotive on Swiss tracks. They were built in 1996 by the Spanish daughter company of the French Alstom group and they are slight modifications of the Spanish state railways RENFE´s series 311, which have been in use in Spain since 1990. It is 14,16 meters long, weighs 73 tons and has a maximum speed of 80 km/h. It is driven by an 8 cylinder V engine, driving a generator which in turn creates electricity to drive the asynchronous electric drive motors at axles. The locomotive is designed for switching work, railroad maintenance work and light cargo train service. SBB has 40 of these engines.
Photo from Porrentruy station 22.6.2002 by Ilkka Siissalo.

The Am 841 locomotives were parked at a difficult place for photography, but this picture still shows the side view of the Spanish engines. SBB got these locomotives very cheaply, but still they have been very well liked, especially since the drivers have a very good view to all directions.
Photo from Porrentruy station 22.6.2002 by Ilkka Siissalo.
Uploaded 23.6.2002.

A similar Am 841 as shown above, but now seen properly from its side.
Picture from Buchs station 3.11.2022 by Ilkka Siissalo.

The diesel locomotive type Am 843 was built by Vossloh and they called this type MaK 1700. It's a very common diesel type throughout Europe. It's not an old machine, but still it seems the red colour used in painting it has lot lasted in the constant sunshine. Here we see this one doing shunting at the Muttenz yard close to Basel.
Picture from Muttenz 5.11.2022 by Ilkka Siissalo.

Another view of the same Am843 diesel. The poor locomotive would surely need a new painting.
Picture from Muttenz 5.11.2022 by Ilkka Siissalo.

Two similar MaK 1700 machines but now in the colours of the SBB subsidiary SBB Cargo. The red one shown above was in the colours of SBB Infra.
Picture from Bern, next to the SBB canteen Weyernmannshaus 1.10.2017 by Ilkka Siissalo.

Earlier this one was called Em 3/3 but now its new type name is Em 830. These were built in two batches (40 machines)for the SBB 1959 to 1963 and also 11 machines were delivered to the SZU Sihltal-Zürich-Ütlibergbahn in 1962. Since then they have been a common sight at many stations. But now lately since individual wagonload cargo is diminishing everywhere and these machines are also getting old, it's soon the last time to get a photo :-) It's a modest machine. Power rating is 441 kW (momentary top power) or just 324 kW continuous power. Top speed is 65 km/h. They have been used in light switching work plus delivering individual wagons to factories.
Picture from Buchs station 3.11.2022 by Ilkka Siissalo.

The Tm 4. series diesel locomotive no. 8755 is built for light switching work by SLM in Winterthur and has a speed of only 45 km/h. It was kept "just in case" at the Swiss station of Rheinfelden.
Photo 4th of June 1999 in Rheinfelden by Ilkka Siissalo.

This is an old diesel switcher/shunter of the type SBB Tm II. Nowadays this model would be called Tm 232, but at the time when this picture was taken it was still Tm II. Note that if you google "SBB Tm II" you get a lot of pictures of a far smaller diesel motor draisine. The same class Tm II was used two times to mean two totally different machines. In the past there have been at least four very different small Swiss diesel locomotives which all have been at some point of time called Tm II. Also the current class Tm 232 contains at least three totally different but modernised locomotives, those that used to be called Tm III, Tm IV plus some bought from private operators and which differed a lot. So don't look too closely at the class number !
The locomotive that we see in the picture was (later than this picture was taken) also called Tm IV. Yes, the naming is a total mess !
These machines were built by SLM in 1970 to 1978. It's a light shunter weighing only 30 tons with a top speed of 30 km/h in shunting mode and 60 km/h when in "line operation" mode. They had a MAN type R8V 16/18 engine, but some of them as they were reclassified from Tm II to Tm IV received Caterpillar's tractor engines. It's a diesel-hydraulic machine. Here we see it as it used to be, before all kinds of modernisations. But please note that the Tm IV shown above used to be exactly this same machine. The one above has been modernised, this one not.
Picture from Oensingen 10.7.2010 by Ilkka Siissalo.

A brand new "rail truck" or diesel engine rail tractor as it is officially classified, the SBB Tm 234 was built in year 2000 and is used for railroad maintenance work. As earlier explained, the Swiss have a habit seen nowhere else in the world that they habitually have one small locomotive, "rail tractor" or other helper engine at each major station. Now many of these Te and Tm series engines have become too old, being from the 1930s-1940s, and are gradually being replaced by newer and better equipment.
Photo from Vallorbe station at 2. Nov. 2001 by Ilkka Siissalo.
Uploaded Jun 6, 2002.

A similar Tm 234 rail truck as above but now some 20 years later. These machines built by Stadler have been very well liked.
Picture from the now decommissioned little station of Haag-Gams in the kanton St Gallen 3.11.2022 by Ilkka Siissalo.

Another Tm 234, here in front of a long track repair train parked at the station of Martigny.
Picture 10.5.2023 by Ilkka Siissalo.

The same machine as above, now seen more from the other side.
Picture from Martigny 10.5.2023 by Ilkka Siissalo.